Fluid sampling apparatus

ABSTRACT

A fluid sampling apparatus comprises a tubular duct of circular or elliptical cross-section, a sampling tube extending into the duct and terminating in an outlet opening, and means for rotating the sampling tube about a rotary axis to cause the inlet opening to sweep a circular area bounded by the internal surface of the tube.

United States Patent Grothe et al.

Jan. 8, 1974 FLUID SAMPLING APPARATUS Inventors: John Grothe, Lakefield, Ontario; Brian Frank Osborne, Peterborough, Ontario, both of Canada Assignee: Milltronics Limited, The Kingsway Peterborough, Ontario, Canada Filed: Apr. 12, 1972 Appl. No.: 243,298

Foreign Application Priority Data Apr. 13, 1971 Great Britain 9,233/71 US. Cl 73/422, 73/424 Int. Cl. G01n l/l0 Field of Search 73/422 R, 424

[5 6] References Cited UNITED STATES PATENTS 2,020,529 11/1935 Thorsten 73/422 R Primary Examiner--S. Clement Swisher Attorney-J. A. Legris [5 7] ABSTRACT A fluid sampling apparatus comprises a tubular duct of circular or elliptical cross-section, a sampling tube extending into the duct and terminating in an outlet opening, and means for rotating the sampling tube about a rotary axis to cause the inlet opening to sweep a circular area bounded by the internal surface of the vtube.

9 Claims, 7 Drawing Figures FLUID SAMPLING APPARATUS This invention relates to fluid sampling apparatus for obtaining representative samples of a fluid flowing through a pipe or duct. The apparatus described herein is primarily intended for use in sampling liquids containing particulate matter, but apparatus in accordance with the invention is generally applicable to the sampling of fluids whether liquid or gaseous, and is especially suitable for the sampling of emulsions and gas/- dust suspensions.

In any process where particulate matter is handled as a suspension in a liquid the obtaining of a representative sample is extremely difficult. The difficulty is caused mainly by the settling of the solid matter, and turbulence in slurry flow which tends to cause particle segregation so that the constituency of the liquid varies across the area of flow. Errors resulting from these effects are compounded when a small, continuous, representative sample is required.

The present invention provides an apparatus which enables a truly representative sample to be obtained notwithstanding variations in constituency of the fluid across the cross-section of flow.

A fluid sampling apparatus according to the present invention comprises a tubular duct of circular or elliptical cross-section having an internal surface and a longitudinal axis, a sampling tube extending into the'duct and tenninating in an inlet opening, and means for rotating the sampling tube about a rotary axis to cause the inlet opening to sweep a circular area bounded by the internal surface of the tube. The inlet opening may be in the form of a sector of a circle, or in the form of a narrow slot extending diametrically across the duct, or may comprise one or more narrow slots extending radially from the duct axis.

In the case of a duct of circular cross-section, the sampling tube must extend axially along the duct axis; such a construction is suitable if the duct is formed with an elbow. In the case of a straight duct where the sampling tube extends into the duct at an angle, the duct must be of elliptical cross-section having an ellipticity corresponding to the angle which the sampling tube subtends to the duct axis.

Three embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:

FIG. 1 is a fragmentary perspective view, partly broken away, of a liquid sampling apparatus according to one embodiment of the invention;

FIG. 2 is a sectional plan view of a liquid sampling apparatus according to the second embodiment of the invention; and

FIG. 3 is a section on line 33 in FIG. 2;

FIG. 4 is a section on line 4--4 in FIG. 2;

FIG. 5 is a section on line 5--5 in FIG. 2;

FIG. 6 is a fragmentary perspective view, partly broken away, of a liquid sampling apparatus according to another embodiment of the invention; and

FIG. 7 is a sectional plan view of a detail of the apparatus shown in FIG. 6.

Referring to FIG. I, the apparatus comprises a tubular duct 10 of circular cross-section having an inlet end 11 and an outlet end 12. The duct is formed with a right angled bend to provide an end wall 13 provided with a rotary seal 14 through which a sampling tube 15 extends. The sampling tube 15 extends along the axis of the duct and is flared at one end to provide a narrow inlet opening 16 which extends diametrically across the full width of the duct. The sampling tube 15 is rotated about its axis by a constant speed motor 17 through a belt and pulley drive 18. As the sampling tube is rotated the inlet opening 16 rotates so as to sweep a circular area bounded by the internal surface of the duct; equal areas of the duct are swept in equal times, thereby diverting along the sampling tube a continuous sample of the liquid which truly represents the average constituency of the liquid. If the pressure within the duct 10 is substantially higher than the pressure at the outlet 19, then it is necessary to place a throttling valve 20 in the sampling tube so as to maintain the sample flow velocity substantially equal to themain flow velocity. In addition, to minimize edge effects which might interfere with the obtaining of a truly representative sample, the flared portion 21 of the sampling tube should constitute a transition region of constant cross-sectional area from the opening 16 to the tube section 15.

Referring now to FIGS. 2 to 5, wherein parts corresponding to those of FIGS. 1 and 2 are denoted by the same reference numerals, the sampling tube 15 extends through a rotary seal 22 in the wall of the duct 10, the duct itself being straight. The rotary axis of the sampling tube is therefore inclined to the duct axis, so that as the sampling tube is rotated about its own axis by the motor (not shown), the inlet opening 16 sweeps a circular area whose projection onto a plane perpendicular to the duct axis is elliptical. In order that the inlet opening should sweep the whole cross-sectional area of the duct, the latter is of corresponding elliptical crosssection in the vicinity of the sampling tube inlet, as will be appreciated from the sectional view of FIG. 4. The duct 10 is shaped so as to provide a circular inlet 11 and a circular outlet 12, which may be fitted with respective pipe coupling members for coupling to the pipe ends in the main liquid system.

The sampling apparatus shown in FIG. 6 comprises a tubular duct 10 of circular cross-section having an inlet end 11 and an outlet end 12. The duct is formed with a 45 angle bend and is provided with an extension 23 housing a rotary seal through which a sampling tube 151extends. The sampling tube 15 extends along the axis of the duct 10 and is rotated about its axis at a constant speed by a constant speed motor 17 through a chain and sprocket drive 18. The arrangement is generally similar to that of FIG. 1. However, in the present embodiment the sampling tube 15 terminates in a flared transition portion 21a providing a terminal inlet opening 16a. The inlet opening 16a instead of being in the form of a parallel-sided slot, is in the form of a sector of a circle corresponding to the circular area to be swept by the opening, the apex of the sector lying on the rotary axis of the tube. The portion 21a, as in the previous embodiments, defines a transition region of constant cross-sectional area.

Owing to the finite thickness of the sampling tube it is difficult in practice to design the inlet opening so as to sweep the region adjacent to the internal surface of the duct accurately. The difficulty can be overcome either by machining the internal surface of the duct so as to form an annular step, or by placing an insert in the duct to form such a step. In the present example, as illustrated in FIG. 7, the internal surface of the duct 10 is formed with an annular step 22, which defines an upstream duct region 23 and a downstream duct region 24. The downstream duct region 24 is of the greater diameter. The sampling tube is located in the downstream duct region with the inlet opening 16a positioned adjacent to the step 22. Thus, as the sampling tube is rotated, the inlet opening 16a sweeps the entire cross-sectional area of the upstream duct region as defined by the step.

It should be noted that, in the case of a sector-shaped inlet opening, if the sampling tube is rotated at constant speed the sweep time at any point in the cross-section to be swept is independent of the radial distance of the point from the duct axis. This modification is especially advantageous where highly segregated slurries are to be sampled.

Particular advantages of the invention are, first that it enables a small sample to be obtained continuously from a closed pipeline; second, that the sample is truly representative since any segregation is automatically compensated; and third, that the apparatus is very simple in its construction and operation.

It will be apparent that the apparatus is readily adaptable for the subdividing of streams other than for sampling purposes.

In a modification of the invention not illustrated, wherein the sampling tube preferably extends axially along the duct, the sampling tube is rotated not by an electric motor and belt drive, but by means of vanes attached to the sampling tube and propelled by the main flow of liquid. In this way the slot may be caused to rotate at a speed which is a function of the main flow velocity.

What we claim as our invention is:

l. A fluid sampling apparatus comprising a tubular duct having an internal surface and a longitudinal axis, a sampling tube extending into the duct, the sampling tube having a terminal inlet opening, a constant speed drive means coupled to the sampling tube for rotating the sampling tube at a constant speed about a rotary axis to cause the inlet opening to sweep an unobstructed circular area bounded by the internal surface of the duct.

2. A fluid sampling apparatus according to claim 1, wherein the duct is of circular cross section, the sampling tube being coaxial with the duct.

3. A fluid sampling apparatus according to claim 2, wherein the internal surface of the duct is formed with an annular step defining an upstream duct region and a downstream duct region of greater diameter than the upstream duct region, the sampling tube being located in the downstream duct region, and the inlet opening being positioned adjacent to the step so as to sweep the entire cross-sectional area of the upstream duct region.

4. A fluid sampling apparatus according to claim 1, wherein the tubular duct is of elliptical cross-section in the vicinity of said inlet opening, the rotary axis of the sampling tube being inclined to the axis of the duct at an angle corresponding to the ellipticity of the duct cross-section.

5. A fluid sampling apparatus according to claim 1, wherein the inlet opening is shaped as a parallel-sided slot extending diametrically across the duct.

6. A fluid sampling apparatus according to claim 1, wherein the inlet opening is shaped as a sector of the circle conforming to said circular area, the apex of the sector lying on the rotary axis of the sampling tube.

7. A fluid sampling apparatus according to claim 1, wherein the sampling tube comprises a tubular portion of circular cross section terminating in a flared portion providing said terminal inlet opening, the flared portion defining a transition region of constant cross-sectional area from the inlet opening to said tubular portion of the sampling tube.

8. A fluid sampling apparatus according to claim 7, wherein the sampling tube includes a valve for restricting the velocity of flow of fluid along the tube to the velocity of flow of fluid along the duct.

9. A fluid sampling apparatus comprising a tubular duct of circular cross-section having an internal surface and a longitudinal axis,

said internal surface being formed with an annular step defining an upstream duct region and a downstream duct region of increased diameter;

a sampling tube extending into the duct along said longitudinal axis, the sampling tube being located in said downstream region,

the sampling tube having a terminal inlet opening positioned adjacent to the step, said inlet opening being shaped as a sector of a circle conforming to the interior cross section of the duct, and

constant speed drive means coupled to the sampling tube for rotating the sampling tube at a constant speed about a rotary axis,

the sampling tube comprising a tubular portion of circular cross-section terminating in a flared portion providing said inlet opening, the flared portion defining a transition region of constant crosssectional area from the inlet opening to said tubular portion. 

1. A fluid sampling apparatus comprising a tubular duct having an internal surface and a longitudinal axis, a sampling tube extending into the duct, the sampling tube having a terminal inlet opening, a constant speed drive means coupled to the sampling tube for rotating the sampling tube at a constant speed about a rotary axis to cause the inlet opening to sweep an unobstructed circular area bounded by the internal surface of the duct.
 2. A fluid sampling apparatus according to claim 1, wherein the duct is of circular cross section, the sampling tube being coaxial with the duct.
 3. A fluid sampling apparatus according to claim 2, wherein the internal surface of the duct is formed with an annular step defining an upstream duct region and a downstream duct region of greater diameter than the upstream duct region, the sampling tube being located in the downstream duct region, and the inlet opening being positioned adjacent to the step so as to sweep the entire cross-sectional area of the upstream duct region.
 4. A fluid sampling apparatus according to claim 1, wherein the tubular duct is of elliptical cross-section in the vicinity of said inlet opening, the rotary axis of the sampling tube being inclined to the axis of the duct at an angle corresponding to the ellipticity of the duct cross-section.
 5. A fluid sampling apparatus according to claim 1, wherein the inlet opening is shaped as a parallel-sided slot extending diametrically across the duct.
 6. A fluid sampling apparatus according to claim 1, wherein the inlet opening is shaped as a sector of the circle conforming to said circular area, the apex of the sector lying on the rotary axis of the sampling tube.
 7. A fluid sampling apparatus according to claim 1, wherein the sampling tube comprises a tubular portion of circular cross section terminating in a flared portion providing said terminal inlet opening, the flared portion defining a transition region of constant cross-sectional area from the inlet opening to said tubular portion of the sampling tube.
 8. A fluid sampling apparatus according to claim 7, wherein the sampling tube includes a valve for restricting the velocity of flow of fluid along the tube to the velocity of flow of fluid along the duct.
 9. A fluid sampling apparatus comprising a tubular duct of circular cross-section having an internal surface and a longitudinal axis, said internal surface being formed with an annular step defining an upstream duct region and a downstream duct region of increased diameter; a sampling tube extending into the duct along said longitudinal axis, the sampling tube being located in said downstrEam region, the sampling tube having a terminal inlet opening positioned adjacent to the step, said inlet opening being shaped as a sector of a circle conforming to the interior cross section of the duct, and constant speed drive means coupled to the sampling tube for rotating the sampling tube at a constant speed about a rotary axis, the sampling tube comprising a tubular portion of circular cross-section terminating in a flared portion providing said inlet opening, the flared portion defining a transition region of constant cross-sectional area from the inlet opening to said tubular portion. 